Plants require a ranger of nutrients, both macro- and micro-, to ensure healthy growth. In certain environments, abiotic constraints preclude the availability of sufficient amounts of these essential nutrients for root uptake via addition of fertilizer to the soil. This can be due to inadequate levels of soluble forms of mineral nutrients in soil solution, water deficit in the top soil, an alkaline soil pH, high soil carbonate content, low organic matter content in soil and other key soil factors that limit nutrient availability.
Grain and seed crops, as well as fruit trees, require rapid and intensive nutrient supply of large amounts of mineral nutrients into flowers, young seeds, pods and fruits, particularly during the reproductive growth stage, which may coincide with declined root vigor and unfavorable soil (e.g., water deficit) and climate conditions (e.g., high temperature), leading to untimely and inadequate nutrient supply to meet this rapid demand. In addition, continual removal of micronutrients in seeds, grains and fruits can deplete the available pool of nutrients in soils. Under these circumstances, the application of foliar fertilizers provides a precise, timely and effective supply of nutrients for plant reproductive organs and at much lower required application rates than soil fertilizers. This can result in not only quick correction or prevention of nutrient disorders and yield losses but also an improvement in crop quality.
Under such conditions, it has been found that foliar fertilization provides great benefits in terms of producing improved yields of healthy plants and crops. Foliar fertilization is the application of liquid fertilizer directly onto aboveground plant parts, rather than to the soil surrounding the plant. The fertilizer is drawn into the plant by penetration through either or both of the stomatal openings and cuticle into the leaf epidermis.
A typical foliar fertilizer may be either a solution of a soluble chemical compound in water or a dispersion/suspension of a non-soluble fertilizing compound in water.
The use of a soluble fertilizing compound facilitates rapid penetration of nutrient ions into the plant and, therefore, provides for efficient correction of nutritional deficiencies. However, the use of a highly soluble fertilizing compound can lead to phytotoxicity and so it can only be applied in very low concentrations through repetitive sprays (for example, two to four sprays from late vegetative growth to reproduction stage). This necessitates the labor-intensive use of a low-dosage fertilizer composition over multiple applications to supply the required amount of nutrients for healthy growth.
Suspension foliar fertilizers are, generally, inorganic mineral compounds, such as oxides and hydroxides, which are finely ground and have relatively low water solubility. Due to their low solubility, they can be applied to plants at higher concentrations without any risk of phytotoxicity. The presence of the low-solubility fertilizing compound on the leaf surface acts as a slow release source, meaning the plant can be supplied with appropriate nutrients over a relatively long period of time after a one-time application process.
In practice, it has been found that the advantages of suspension foliar fertilizers are tempered by issues of poor distribution on the leaf surface as well as availability of the low-solubility fertilizing compound sometimes being inadequate. Further, since the fertilizing compound, after application, is left behind as a fine solid on the leaf surface, it may be prone to being washed or blown off that surface by the elements.
There is a need for an improved foliar fertilizing composition to facilitate efficient and reliable supply of desired nutrients to a plant.